IEEE 802.16m protocol requests that service delay should be further reduced as compared to the current IEEE 802.16e to better support delay-sensitive services, such as voice service, real-time gaming, real-time video stream service or high priority E-commerce, etc. Those delay-sensitive services usually require a data delay between BS and MS less than 10 ms in uplink and downlink directions.
There are several existing bandwidth request and allocation mechanisms in IEEE 802.16e protocols, such as Unsolicited Grant Service (UGS), real-time Polling Service (rtPS), and Extended rtPS (ertPS).
The resource allocation manner of UGS technology is shown in FIG. 1, wherein a mobile terminal doesn't need to request any resource, instead, after the establishment and before the end of a service, the base station automatically allocates predefined resource, such as time-frequency resource block, for the service of the mobile terminal after the startup of each allocation cycle. Wherein, for established service which is not ended, taking voice telephone service as example, when both parties involved do not speak during the communication, there is no uplink transmission between the mobile terminal and its dominating base station, however, the service is still active and is allocated with resources, namely, if one party begins to speak, the other party will hear its speech immediately. The voice telephone service won't end until, one party hangs up or severe signal problem or network fault comes forth.
Wherein, in case that each allocation cycle of UGS comprises a number of physical layer frames, the above resource allocation manner of UGS could be comprehended as following: allocating a time-frequency section in one, several or all of the uplink sub frames to the mobile terminal for the transmission of the uplink service data belonging to the service.
It is thus clear that, UGS meets the demands of real-time services concerning delay well, however, this manner similar to static allocation undoubtedly causes relatively serious resource waste, since the uplink service data is not transmitted all the time after the establishment of the service.
Different from UGS, rtPS enables the base station to allocate variable amount of resource to a mobile terminal for a service, as shown in FIG. 2. The base station allocates resource for sending bandwidth request (BR) message and resource for sending uplink service data after the beginnings of each allocation cycle. Hereinafter, the sum of the two kinds of resources is referred to as uplink transmission resource.
Wherein, a mobile terminal could generate the BR message according to the amount of its actually cached uplink service data to be transmitted, and report the BR message to the base station. The base station could dynamically adjust the uplink transmission resource allocated to the mobile terminal for the service according to the received BR message, which is in fact to adjust the amount of the part, in the uplink transmission resource, for transmitting the uplink service data.
Thus, rtPS optimizes the utilization of resource over UG. However, rtPS causes more signaling overhead, since it requires a mobile terminal to continually send BR messages (with a size of 6 bytes) to the base station.
The ertPS scheme, based on periodic allocation for uplink transmission resource, unites the advantages of UGS and rtPS. As shown in FIG. 3a, the ertPS scheme doesn't only enable the base station to allocate resource to a mobile terminal without request as in UGS, so that the demand of delay is satisfied, but also allows the mobile terminal to let the base station adjust the amount of resource periodically allocated to it by means of requests. For example, a mobile terminal writes its expected new resource allocation amount into the Extended Piggyback Request field in a Grant Management Subheader (GMSH) following to a Generic MAC header, or into the Bandwidth Request field, i.e. the BR message, in a MAC header having the function of resource request. As shown in FIG. 3, the BR message, aperiodically sent in the resource block shared by uplink service data and BR message allocated by the base station, respectively affects the amount of uplink transmission resource allocated to the service in one or more following allocation cycles.
Wherein, the base station won't change allocation concerning a mobile terminal until it receives a new request of requiring changing the amount of allocated resource from the mobile terminal.
During an allocation cycle, if the standby uplink service data of a mobile terminal is fully transmitted, the mobile terminal will request the base station to adjust the amount of allocated resource to zero, so as to provisionally release the resource occupied by the service. Subsequently, the service comes into silent status. And then, the base station could allocate resource to neither the uplink service data nor the BR message, or could only allocate resource to the BR message. Wherein the resource allocated to BR message is dedicated to the service of the mobile terminal, namely non-contention resources. In case that the base station allocates the above non-content ion resources to BR message, when the standby uplink service data belonging to the service of the mobile terminal comes forth again, the mobile terminal will generate a BR message and send it to the base station by means of the non-contention resources, so as to inform the base station that the service ends the silent status and the base station should periodically allocate uplink transmission resource to it again.
On the contrary, in case that the base station does not allocate resource to BR message, when the standby uplink service data belonging to the service comes forth again, in order to inform the base station about it so that the base station could allocate corresponding resource to the mobile terminal, the following schemes could be adopted by the mobile terminal according to existing ertPS scheme:                to send CDMA code for competing for resource by use of contention resources        
The so called contention resources are those resources without specific occupier, and available to be competed for by multiple mobile terminals. Because wireless transmission resource is very valuable, each mobile terminal generally uses some information with small size and function of identity identifier or even service identifier, such as CDMA code, to compete for the usufruct of contention resources, instead of using an entire data packet as in wire communication protocol CSMA/CD.
With reference to FIG. 3b, wherein, a mobile terminal requests uplink transmission resource from the base station via BR message v, accordingly, the base station allocates resource block w to the mobile terminal for transmission standby uplink service data x′ and the next BR message y′. When x′ is carried by w, there is no standby service data in the buffer of the mobile terminal, therefore, resource requested by the mobile terminal in y′ is zero. For example, it is a typical condition of a voice communication service coming into silent status on uplink that the user of the mobile terminal does not speak.
Thus the service of the mobile terminal comes into silent status, and the base station no longer allocates uplink service data transmission resource to the service or non-contention resources to BR message. In conjunction with the above example of voice communication service, when the user of the mobile terminal speaks again, standby data l′ will be locally generated, therefore the mobile terminal transmits, on the preassigned ranging channel m′, a CDMA code n′ for competing for non-contention resources, to request for the usufruct of non-contention resources. Since contention resources are obviously deficient compared to the amount of information of resource requests sent the services of a large numbers of mobile terminals, it is likely to happen that multiple mobile terminals compete for the usufruct of contention resources at the same time, accordingly, it is likely that one or more mobile terminals could not take the chance of using contention resources at the very first time, thereby the mobile terminal needs to retransmit the CDMA code n′ on the ranging channel many a time. The delay caused therefrom is usually as tens of times long as the upper limit of acceptable delay of delay sensitive services.
In the case as shown in FIG. 3b, the mobile terminal successfully take the usufruct of contention resources, therefore the base station allocates resource o′ to it for transmitting BR message, the mobile terminal accordingly transmits BR message p′ to the base station, and finally obtain resource block q′. At the beginning of the next allocation cycle, the base station will allocate a resource block r′ of default size for the service of the mobile terminal, for transmitting new standby data s′ and new BR message t′.                to send identifier code for requesting to restart allocation of uplink transmission resource by use of CQICH        
CQICH is the channel exclusively used for reporting the information such as the reception quality of downlink signal by the mobile terminal, and when the base station receives the identifier code transmitted by the mobile terminal on such channel(s), the base station will reallocate uplink transmission resource to the mobile terminal.
However, there exist some condition(s) for a mobile terminal to use CQICH, so that the appearance frequency of CQICH could not usually satisfy the strict demands of delay sensitive services, thus occurs unacceptable delay.
The above solutions in prior arts have respective defects summarized as following:
1. UGS
Certain amount of uplink transmission resource is allocated for service in each allocation cycle, although the delay demand of service is satisfied, the utilization efficiency of resource is sacrificed. No matter whether there is standby uplink service data in a period of time, certain amount of resource is occupied, so that the whole resource efficiency of the system is very low.
2. rtps
The amount of allocated resource could be dynamically adjusted compared to UGS and resource waste is decreased, but the mobile terminal must send a BR message in each allocation cycle, frequent transmission of BR messages causes comparatively high signaling overhead, which obviously does no good to resource efficiency.
3. ertPS
The ertPS based on periodic allocation as shown in FIG. 3a has the basically same defect as that of UGS, namely the resource waste is relatively severe.
The ertPS with competition as shown in FIG. 3b has the defect that, when a mobile terminal send CDMA code for competing for contention resources by use of ranging channel, it may not obtain allocated resource or at least may not obtain allocated resource in time due to competition failure, so as to cause big delay, even to cause service interruption. When a mobile terminal uses CQICH to carry identifier code for requesting uplink transmission resource allocation, the high demand concerning delay of delay sensitive service could not usually be satisfied since CQICH is sparsely distributed along the time axis,